A backlight module is usually applied to a display device or a luminous input device. For example, most electronic devices are equipped with display devices for providing a prompting function. According to the contents shown on the display devices, the user may realize the current operating statuses of the electronic devices. Generally, a display device comprises a backlight module and a display panel. The backlight module is used for providing a light beam and guiding the light beam into the display panel. When the light beam is transmitted through the display panel, the corresponding content is shown on the display panel. On the other hand, the luminous input device comprises a backlight module and an input interface. The input interface is for example a keyboard device, a handwriting device or a touch panel. The backlight module is used for providing a light beam and guiding the light beam into the input interface. Consequently, the input interface has a luminous function, and the input interface is visible by the user.
Hereinafter, the structure of a conventional backlight module will be illustrated with reference to FIG. 1. FIG. 1 is a schematic side view illustrating a conventional luminous keyboard device. The conventional luminous keyboard device is disclosed in for example Taiwan Patent No. M419971. As shown in FIG. 1, the conventional luminous keyboard device 100 comprises a light guide plate 110, plural light sources 120, a transparent layer 130, a keycap layer 140, plural light intensity adjusting patterns 150, a reflective layer 160, and an adhering layer 170. The light guide plate 110 has plural openings 112. These openings 112 are located at predetermined positions of the light guide plate 110. Each light source 120 is aligned with a corresponding opening 112. In addition, each light source 120 is disposed within the corresponding opening 112. The transparent layer 130 is disposed over the light guide plate 110. The keycap layer 140 is disposed over the transparent layer 130. The plural light intensity adjusting patterns 150 are disposed on the transparent layer 130. The positions of the light intensity adjusting patterns 150 are determined according to the positions of the light sources 120.
The light source 120 is a light emitting diode or any other appropriate dot light source. The transparent layer 130 is made of polyethylene terephthalate (PET) or any other appropriate transparent material. Please refer to FIG. 1 again. After the light beams emitted by the light sources 120 of the luminous keyboard device 100 are introduced into the light guide plate 110, these light beams are transformed into a planar light beam. The planar light beam is transmitted through the transparent layer 130 overlying the light guide plate 110 and directed to the keycap layer 140. Consequently, plural keycaps (not shown) of the keycap layer 140 are illuminated.
FIG. 2 is a schematic top view illustrating the transparent layer, the light intensity adjusting patterns and the adhering layer of the conventional luminous keyboard device as shown in FIG. 1. Please refer to FIGS. 1 and 2. The light intensity adjusting patterns 150 are arranged between the transparent layer 130 and the keycap layer 140. The light intensity adjusting patterns 150 are partially disposed on the transparent layer 130 and located at the positions corresponding to the light sources 120. Moreover, the light intensity adjusting patterns 150 are arranged around corresponding light sources 120, respectively. By the light intensity adjusting pattern 150, a portion of the light beam near the light source 120 is blocked from being transmitted through the keycap layer 140. Consequently, the intensity of the portion of the light beam transmitted through the keycap layer 140 is not too strong. Under this circumstance, the luminous efficacy of the luminous keyboard device 100 is more uniform.
Generally, the light intensity adjusting pattern 150 is a white reflective pattern. By the light intensity adjusting pattern 150, the light beam from the light source 120 is reflected back into the light guide plate 110. Consequently, the light utilization efficacy is enhanced. Moreover, by the light intensity adjusting pattern 150, the light beam from the light source 120 is prevented from being directly projected onto the keycap layer 140 over the light source 120. Under this circumstance, the intensity of the light beam at local areas is not too strong. Alternatively, the light intensity adjusting pattern 150 is an opaque pattern. For example, the light intensity adjusting pattern 150 is a light-absorbing pattern by coating a black paint on the transparent layer 130. Consequently, the light beam from the light source 120 can be absorbed by the light intensity adjusting pattern 150, and the portion of the light beam to be transmitted through the keycap layer 140 is reduced. Consequently, the intensity of the light beam at the local area of the keycap layer 140 over the light source 120 is not too strong.
As shown in FIG. 1, the reflective layer 160 is disposed under the light guide plate 110. By the reflective layer 160, the light beam from a bottom surface of the light guide plate 110 is reflected back into the light guide plate 110. In other words, the use of the reflective layer 160 can enhance the light utilization efficacy. Moreover, the adhering layer 170 is arranged between the keycap layer 140 and the transparent layer 130. Via the adhering layer 170, the keycap layer 140 and the transparent layer 130 are combined together. As shown in FIG. 2, the light intensity adjusting patterns 150 are separated from the adhering layer 170 (i.e. an adhesive). As the consequently, the light adjusting functions (e.g. light-absorbing function or the light-reflecting function) of the light intensity adjusting patterns 150 will not be influenced by the adhering layer 170. However, after the light beam is transmitted through the light guide plate 110 and the transparent layer 130, the light beam is directed upwardly from the whole transparent layer 130. When the light beam is transmitted through the adhering layer 170, the intensity of the light beam is diminished by the adhering layer 170. Under this circumstance, the luminous efficacy of the luminous keyboard device is deteriorated.
Therefore, there is a need of providing a backlight module, in which the luminous efficacy is not adversely affected by the adhesive.